Talk:Resonant inductive coupling

Rename article
I think I'm going to move the article ["Resonant energy transfer"] to resonant inductive coupling or resonant transformer. It seems to be a better name; there's other resonant energy transfers that are not inductive.- Wolfkeeper  23:57, 12 November 2009 (UTC)
 * I agree. One method of "Resonant energy transfer" is "resonant inductive coupling." Two other methods of "Resonant energy transfer" are "Electrical conduction" by means of a "Terrestrial transmission line with atmospheric return circuit" and "Electrical conduction by means of a "Terrestrial single-conductor surface wave transmission line." Because the article or page "Resonant energy transfer" deals exclusively with the "Resonant induction method" it should be renamed or moved to "Resonant inductive coupling." -- GaryPeterson (talk) 16:42, 28 November 2010 (UTC)
 * I think that this phenomenon is similar with the micro power transformer magnetic characteristics. So It should be called "Synchronized Magnetic Phase Coupling". Please refer this URL. --Neotesla (talk) 08:52, 15 June 2014 (UTC)

Re-writing Coupling Coefficient subheading
The sub-heading 'Coupling Coefficient' needs re-writing. Simply look to the first sentence to see why:

"Well misunderstood, the coupling coefficient is often said to be the ratio of flux interlinking to the secondary coil, but it is a misunderstanding."

There's no reason at all to suggest a misunderstanding in an informative article, never-mind book-ending it like that.

The section is also unclear at points: "The coupling coefficient is fixed by the positional relationship between the coil and the coil."

and uses a lot of unexplained technical language: "the coupling coefficient does not change between when the system is in the resonance state and when it is not in the resonance state, but the ratio between the mutual flux and the leakage flux changes greatly."

There are also no citations anywhere in the section.

I would edit this myself, but I do not have sufficient experience to be able to explain these terms.

209.6.37.209 (talk) 15:55, 28 December 2016 (UTC)


 * I've removed that first sentence which is plain WP:WEASEL but I don't think it has helped much. The closest it ever comes to actually defining anything is "the coupling coefficient is the ratio to the component that becomes mutual inductance in the coil inductance".  Not at all clear to me whether that is the same as the usual definition of M/root(L1L2).  A ratio is a ratio between two things and "the component that becomes mutual inductance" is only one thing. SpinningSpark 00:30, 8 January 2017 (UTC)


 * The coupling coefficient in electromagnetism is the ratio of inductance. This is obvious by looking at the diagram of the equivalent circuit of the transformer and we can be easy understood by referring to the several formura. If necessary I will be possible to indicade a lot of literature. And the coupling coefficient does not directly indicate the magnetic flux ratio.118.236.168.22 (talk) 04:03, 8 January 2017 (UTC)
 * The ratio of what inductances? The self-inductances of the two windings?  That's not going to give sensible results; the coupling coefficient won't change if you put one coil on the Moon and leave the other on Earth.  So please, state this as a proper mathematical expression in terms of the measurables of the circuit, or else link to an online source that does so.  Otherwise, I'm inclined to wipe the whole section and replace it with something that makes sense. The inductance article makes a much better fist of this. SpinningSpark 10:47, 8 January 2017 (UTC)
 * The description of the leakage factor which is in the article of the leakage inductance is not good at all. Very rudimentary mistakes were found. The dimensions of the physical quantity did not match in the formula. Inductance ratio is the ratio of mutual inductance and leakage inductance. First the following formula was shown.
 * σP = ΦPσ/ΦM = LPσ/LM
 * σS = ΦSσ'/ΦM = LSσ'/LM
 * The dimensions of the physical quantity of the magnetic flux is,
 * kg m2 s-2 A-1
 * The dimension of the inductance is,
 * kg m2 s-2 A-2
 * Obviously the dimensions are different. So I reviewed it as follows,
 * $$\sigma_{P}=\frac{\phi_P^\sigma}{\phi_M}=\frac{L_P^\sigma i_P}{L_M i_M}$$
 * $$\sigma_{S}=\frac{\phi_S^\sigma}{\phi_M}=\frac{L_S^\sigma i_S}{L_M i_M}$$
 * The dimensions are now matched. And it became a general relational expression that appears in many textbook. Is it necessary to present any literature on this general formula?118.236.168.22 (talk) 11:40, 8 January 2017 (UTC)
 * I searched for a while, and I found a source which is simply described about the relation of inductance, winding current and flux.
 * $$\phi=L I$$
 * 118.236.168.22 (talk) 12:16, 8 January 2017 (UTC)
 * We don't seem to be getting any closer to a definition of coupling coefficient. SpinningSpark 14:36, 8 January 2017 (UTC)
 * If Cblambert does not Insist his own creation about the Leakage factor, the difinition of the coupling coefficient has no problem as follows,


 * Leakage_inductance


 * $$L_{oc}^{pri}=L_P=L_P^\sigma+L_M$$
 * where
 * $$L_P^\sigma=L_P\cdot{(1-k)}$$
 * $$L_M=L_P\cdot{k}$$
 * and
 * $$L_{oc}^{pri}$$ = Primary inductance
 * $$L_P$$ = Primary self-inductance
 * $$L_P^\sigma$$ = Primary leakage inductance
 * $$L_M$$ = Magnetizing inductance referred to the primary
 * Leakage factor is not related to coupling coefficient. In this article, it is sufficient to state that the value of the coupling coefficient does not change even if it resonates or does not resonate.118.236.168.22 (talk) 15:38, 8 January 2017 (UTC)
 * You keep banging on about leakage factor not being relevant. That is half the problem with this article, it talks about what is not relevant ahead of talking about what is, and never quite gets to the point.
 * You have not given a definition in terms of measurables. You have used coupling coefficient to define a new thing (magnetizing inductance) which is not a measurable. I prefer the explanation in the inductance article which defines mutual inductance and coupling coefficient in terms of the two-port voltages and currents.  I think the best solution is to reduce the description here to a sentence giving the definition in the inductance article and link that as main article.  There is no point in having the same thing described in detail in two places, especially as one of them is so badly done. SpinningSpark 16:48, 8 January 2017 (UTC)
 * At here, we need to think about the purpose of using the coupling coefficient. Even with the same content, the explanation will be different if it is described mathematically, academically or explained to the electronic design engineer. The above link to the coupling coefficient is not academic, but very practical. The important thing is that there is no theoretical contradiction between there. The coupling coefficient in this article have to be consistent with them, but furthermore it is necessary to adapt the expression and the explanation for the purpose of understanding wireless power transfer. As it is written by several writers, it is very coarse so far, but it will be a useful section by enriching links in this field.121.2.184.184 (talk) 01:58, 9 January 2017 (UTC)
 * "Magnetizing inductance referred to the primary" is written by another writer and I would like to write "Mutual inductance referred to the primary" if it is me.121.2.184.184 (talk) 02:22, 9 January 2017 (UTC)
 * What does that even mean? A transformer is a reciprocal device which leads to mutual inductance being numerically equal in both directions.  There is no "referred to the primary".  That phrase only has meaning for impedances that originate on the secondary and are transformed by the transformer ratio as seen from the primary.  That does not apply to mutual inductance.  Yes, you can use the coupling coefficient to divide the inductance into a part that couples and a part that does not (your comment about how these have been named really doesn't matter for this discussion) but that does not mean you can use that as a definition of coupling coefficient.  Those inductances don't really exist, they are purely notional.  You can't connect a voltmeter on the node between them because it doesn't actually exist.  So I say just say in this article that you are notionally dividing the inductance by the coupling ratio and link to the inductance article for an explanation of coupling coefficient.  The diagram has to go as well, marking the k fraction of the inductance as M (implying mutual) is just plain wrong. <b style="background:#FAFAD2;color:#C08000">Spinning</b><b style="color:#4840A0">Spark</b> 14:31, 9 January 2017 (UTC)
 * Probably I think that it is better to do it according to your thinking as to the correction of this part. I just wanted to correct the description that "the coupling coefficient is the fraction of the flux of the primary that cuts the secondary coil". Because it means that "the ratio of the effective flux reaching the secondary side of the total flux generated at the primary side".121.2.184.184 (talk) 16:43, 9 January 2017 (UTC)

Ratio of mutual flux and leakage flux
I have removed this from the article "but the ratio between the mutual flux and the leakage flux changes significantly. Specifically, mutual flux increases significantly when the system is in a resonant state." Why do we need to say this? The transformer coupling coefficient is defined purely in relation to the transformer, not the resonant circuits. It is defined under open circuit conditions (so there can be no question of resonance) and under open circuit conditions the ratio of leakage and mutual flux does stay constant with applied voltage. It can only get to be different if a load is applied. True, that load can be a resonating capacitor, but stating this in the section about the transformer is very misleading. <b style="background:#FAFAD2;color:#C08000">Spinning</b><b style="color:#4840A0">Spark</b> 16:38, 9 January 2017 (UTC)
 * You mentioned the description as "This leads to the voltage appearing at the secondary being less than predicted by the turns ratio of the windings.", but in WPT (wireless power transfer), it is the "Resonant inductive couplingIng" that there is a phenomenon that the voltage is higher than the predicted turns ratio.--121.2.184.184 (talk) 17:04, 9 January 2017 (UTC)
 * Not under secondary open-circuit conditions there can't, because there can't be any resonance in the first place. <b style="background:#FAFAD2;color:#C08000">Spinning</b><b style="color:#4840A0">Spark</b> 17:11, 9 January 2017 (UTC)
 * Then, it is better to supplement that a voltage higher than the voltage expected by the turns ratio appears on the secondary side when the system is in the resonance state. And I think that the description you corrected is beautiful.--121.2.184.184 (talk) 17:20, 9 January 2017 (UTC)

The diagram of Resonant coupling
The parallel capacitor Cs on the primary side has no meaning. It should be removed. Only the resonance capacitor of the secondary side has meaning.--121.2.184.184 (talk) 17:37, 9 January 2017 (UTC)


 * Take a look at double-tuned amplifier. <b style="background:#FAFAD2;color:#C08000">Spinning</b><b style="color:#4840A0">Spark</b> 21:26, 9 January 2017 (UTC)


 * There is one question, The Double-tuned amplifier and the Resonant inductive coupling of the wireless power transfer are a little different. The primary side resonant circuit of the indicated link is working effectively. Because the collector of the transistor is high impedance, so the power source as seen from the resonant circuit of the primary side is the constant current source. On the other hand, in the case of wireless power transfer, it is a voltage source and it is driven by a bridge circuit with low impedance. In this case, large pulse currents flows in the parallel capacitor of the primary side, causing heat generation and destruction of the element. The difference between whether the power source is a constant current source or a voltage source is very inportant. Therefore, it is one of a common mistake to refer to the Double-tuned amplifier for wireless power transfer.--121.2.193.122 (talk) 09:58, 10 January 2017 (UTC)
 * This article is a general article. It actually gives IF tuning (ie double tuning) as an application in the lead.  It should not, therefore, be assuming any particular type of source.  That could be given as an example, but the article shouldn't be limited to that. <b style="background:#FAFAD2;color:#C08000">Spinning</b><b style="color:#4840A0">Spark</b> 15:49, 10 January 2017 (UTC)
 * If it is so, all WPT relational descriptions such as resonant transformer, Qi power transfer, WiTricity, Rezence etc., will have to be removed entirely.--121.2.169.188 (talk) 03:46, 11 January 2017 (UTC)

Diagrams
It would be nice to explain why there are coils that are not connected to the load, and in the diagram of the Soljačić system, not connected to the oscillator? Are these somehow massaging the magnetic field so it acts more strongly on the coils that are connected, or is this an error in diagramming? -- Beland (talk) 15:30, 11 January 2018 (UTC)
 * I think that Soljačić does not correctly understand the principle of a resonant transformer. Therefore he considers the resonator of the primary side and the resonator of the secondary side indispensable. And he argues in his paper that there is a new "resonance field phenomenon" between the two resonators which is not in the theory so far.
 * Is it really sure?
 * It is obvious that his idea is inspired by the phenomenon that power transmission occurs when two Tesla coil systems are brought close together.--Discharger1016 (talk) 20:00, 22 April 2018 (UTC)

Resonance mechanism poorly described and invasive dogmatic content
In this page the resonance mechanism is suggested to improve the coupling factor whereas it is only a way to reduce losses on both the generator side and the load side for the same field level as it is also explained somewhere in the page. Resonance is a first consequence of the impedance matching process, it is similar for all types of couplings ( mechanical, acoustic, magnetic, electric) and consists in compensating a reactive link impedance by a conjugate reactance, see for instance: https://en.wikipedia.org/wiki/Impedance_matching and in particular the 'Maximum power transfer matching' subsection. All this is well known for centuries and well described in many old books, see for instance VACUUM TUBE AMPLIFIERS Copyright, 1948, by the McGraw-Hill Book Company, Inc, chapter5 pp201 to 226, for a direct reading see https://www.jlab.org/ir/MITSeries/V18.PDF. This book summarized works done well before (before 1937 at least). The link is not affected by the resonance effect that is an internal process in the devices, the coupling factor 'k' is a constant that doesn't depend on frequency but only on distribution of charge and currents (then electrodes and coils geometry). The appropriate quantity to take into account the "resonance" effect is the coupling index 'kQ' introduced in the bottom of page 202 in the book. It is also introduced in this page under a new name "factor of merit" that if not inappropriate but somehow hides the historical succession of events. Chapter 5, also address the asymmetry between coils Q-factors 'Q1, Q2' (the second resonance awkward idea). The two introduction figures are then dogmatic according to me as they indicate a sort of focalization of field lines whereas, as explained, resonance does not affect coupling 'k' and field line distribution or it should be proved with actual data. The chapter "Witricity resonant...." where the coupling index is introduced is totally commercial. The commercial name "Witricity" should not figure here as the information introduced apply for all resonant systems. By the way, according to me the only specific aspect of the Witricity patent is the use of two core-less transformers on both side to provide resistance tuning. The whole tuning process is two fold reactance and resistance tuning as explained in the following didactic videos I made a few years ago when teaching the field in University: https://www.youtube.com/watch?v=yKmseA3Fd-g for inductive coupling and https://www.youtube.com/watch?v=YegIW-1hbvQ for capacitive coupling. Finally the dipole field admittedly decreases as 1/r3, evanescent waves and field (exponential decrease) are only obtained at the interfaces between two mediums. Considering that a magnetic transformer is based on evanescent wave whereas it can be described accurately by non propagating field (quasi-static approximation) is totally inappropriate, dogmatic and doesn't fit with the Okkam razor principle. According to me, this page was well written up to January 2017, then it was turned into some form of advertising for a given company and became more and more dogmatic with time (the awkward figures introduction used to defend a dogmatic content), the use of evanescent field suggesting that the idea is new. Besides the duality theorem that states that a dual capacitive coupling implementation exist (at least theoretically) is totally avoided in the page and I think creating a specific resonant capacitive page would not be an example of good practice. I am afraid that a personal direct contribution on the page will be perceived as non neutral, I am involved in many articles, patents concerning non-radiating near-fields and longitudinal capacitive coupling (resonant of course).Henri BONDAR (talk) 06:39, 10 January 2019 (UTC)

I suggest tagging this article for non neutral point of view (WP:NPOV policy). As said I don't think adding a Resonant capacitive coupling page is a good idea. As an expert in non-radiating near-field applications, I suggest to separate clearly the coupling aspects as well described in the https://en.wikipedia.org/wiki/Coupling_coefficient_of_resonators page, from resonance considerations that are specific implementations in the loads and generators devices and not specific to Witricity patent as falsely suggested here. They can be introduced straightforwardly using impedance matching considerations (see: https://en.wikipedia.org/wiki/Impedance_matching#Maximum_power_transfer_matching) and the coupling index kQ as introduced at least since 1937 in MacGraw-Hill book reference.Henri BONDAR (talk) 13:33, 12 January 2019 (UTC)
 * Still no one to remove these hawful pictures and this dogmatic content from Wikipedia ? There is no place for such dogmatic and NPOV content here ! As already explained; coupling between coils or dipoles in vacuum or air is not affected by resonance (the link itself is not frequency dependent) coupling between distant coils is well described in the specific page (see my comment above). Resonances only reduce the losses in the generator (or load or both) for the same amount of transferred energy or said otherwise allows increasing the amount of power transfer (by either a voltage or current increase) for the same amount of losses. Said otherwise it is a pure matter of quality inside the devices themselves. The pictures showing that field lines distribution are somehow altered by resonances belong to pure phantasm and have nothing to do with actual field lines that again (louder this time) ARE NOT AFFECTED BY RESONANCES !!!!.Henri BONDAR (talk) 12:18, 26 December 2019 (UTC)


 * Agree with the above critique as far as I can understand it. More generally, the article focuses with WP:undue weight on one specialized application of resonant transformers, power supplies and single resonant transformers. A WP:NOTHERE WP:SPA editor who manufactured resonant CCFL power supplies turned this page into his private playground.  Most of it should be deleted and rewritten. I would like to do it but I have a big backlog of articles I am already working on. --Chetvorno<i style="color: Purple;">TALK</i> 06:50, 19 February 2022 (UTC)
 * Maybe you don't know the effect of resonating only the secondary side. The description about CCFL has been corrected in the wrong direction. The description of the TDK patent I presented should also be very helpful.--Neotesla (talk) 01:44, 20 February 2022 (UTC)


 * Wow, the History section is also totally inadequate, it leaves out Karl Ferdinand Braun and almost all of the history of double tuned transformers in radio. This guy really had tunnel vision. --Chetvorno<i style="color: Purple;">TALK</i> 07:00, 19 February 2022 (UTC)
 * I'm not the one who leaves out the history of double tuned transformers in radio. That field you say is the field of telecommunications or high frequency amplifier circuits. Now this discussion is a mix of those fields and power electronics field writers. This is an interesting situation, and it will be a very constructive discussion if each person shares their knowledge. I suggest that this discussion be divided into four cases: analog drive cases with a large drive side impedance, power switching cases with a drive side impedance of zero, and large or small coupling coefficient cases. Then, I think that neither discussion will conflict with each other.--Neotesla (talk) 00:17, 26 February 2022 (UTC)


 * Before the discussion gets confused, I just put on the conclusion first. There is a boundar that at the coupling coefficient is low, the double tuning circuit is practical, and at it is high, resonance only on the secondary side is more practical. Moreover, the double tuning circuit in the high freaquency amplifier circuit is no needed to consider the efficiency. On the other hand, in power electronics, efficiency is considered. It depends on the impedance of the load, I think that k = 0.1 or k = 0.2 is the border. In power electronics, the area of close coupling of a double-tuned circuit is extremely bad efficiency and the FET may be damaged. In such a case, it is better to remove the resonance circuit on the primary side. Is this likely to give sepalate direction to discussions and criticism?--Neotesla (talk) 02:51, 20 February 2022 (UTC)

I agree with a number of points made here. Note that I have recently entered the wireless power transfer space, which is what brought this article to my attention, and Witricity is a competitor with the company I work for. Even still, repeated references to Witricity (or any particular wireless power transfer company which is not historically significant in general consensus) seems commercial and very out of place. Use of the terminology "evanescent" has commercial benefit for Witricity, and in the past they have used that terminology (which is non-standard) to add credibility to e.g. their patents. Impartial background investigation is warranted, though I don't have any references on hand. This isn't to accuse Witricity of editing the page themselves, but it's obvious that their work was a major influence on the article, and unnecessarily so. It is not an impartial article, and the content does not belong in an encyclopedic reference. There was also a noted shift in content quality and impartiality in the closely related article on evanescent waves, where the definition of evanescent has become increasingly ambiguous since about 2015.

The discussion by Henri above certainly is sound, but if I had to disagree with any point, it would be the quibble with the field lines. Resonance does change the field intensity near a receive coil, but only in the same way that input impedance matching increases the field intensity at the transmitter - the power transfer from generator to transmit coil is necessarily larger so of course the field is stronger. But observe that when a receive coil in a resonant circuit is placed into the field, the only way for the received signal strength to increase, is for the magnetic field intensity to increase inside the loop. Put another way, reactive energy stored in the resonant circuit has a significant impact on the local H field around the receive coil, via increased loop current. The power transfer to the receive circuit from the receiving coil is also dependent on impedance matching, but this is a distinct effect.

It's hard to separate the receive circuit from the transmit coil circuit. Above, I mean that the magnetic field at some position in space is hardly changed when a receive coil is introduced, whether the loop is shorted or open, but if you put a resonant capacitor in series with the receive coil (with a closed loop), the magnetic field strength inside the loop is dramatically increased relative to the transmit coils field contribution. The contribution to the field from the transmit coil is not changed, but the reactive energy stored in the resonant network contributes significantly as well.

Comments from others are encouraged. Sjgallagher2 (talk) 19:23, 22 October 2021 (UTC)
 * I have just participated in the wireless power transfer field. This is a coincidence. After all, I also have a competitive relationship with WiTricity. I agree with your view of the Evanescent Field. This has a lot to do with their patents.
 * By the way, the fact that sufficient power can be supplied by resonating only the secondary side is the fact that TDK in Japan has applied their patent and is shown in patent specification (JPA_2012182980). Please refer to this as a physical fact. Of course I did the same experiment and understand that their mention is correct.
 * By the way, WiTricity has filed a patent infringement lawsuit toward Momentum Dynamics regarding wireless power transfer. As a result, this description and facts of TDK have become very delicate. Do I need to mention the reason?
 * The following is a literal translation.
 * [0084]
 * [Third Embodiment]
 * FIG. 19 is a principle diagram of the wireless power transmission system 100 according to the third embodiment. The wireless power transfer system 100 in the third embodiment also includes a wireless power feeding device 116 and a wireless power receiving device 118. However, the wireless power receiving device 118 includes the power receiving LC resonance circuit 302, but the wireless power feeding device 116 does not include the power feeding LC resonance circuit 300. That is, the feeding coil L2 is not a part of the LC resonance circuit. More specifically, the feeding coil L2 does not form a resonant circuit with other circuit elements included in the wireless feeding device 116. No capacitor is inserted in series or in parallel with the feeding coil L2. Therefore, the feeding coil L2 is non-resonant at the frequency at which electric power is transmitted.
 * [0085]
 * The power supply VG supplies an alternating current having a resonance frequency fr1 to the feeding coil L2. The feeding coil L2 does not resonate, but generates an AC magnetic field having a resonance frequency fr1. The power receiving LC resonance circuit 302 resonates due to this AC magnetic field. As a result, a large alternating current flows through the power receiving LC resonance circuit 302. Through the study, it was found that it is not always necessary to form an LC resonant circuit in the wireless power feeding device 116. Since the feeding coil L2 is not a part of the feeding LC resonance circuit, the wireless feeding device 116 does not move to the resonance state at the resonance frequency fr1. Generally, in magnetic field resonance type wireless power transfer, a resonance circuit is formed on both the power supply side and the power reception side, and each resonance circuit is resonated at the same resonance frequency fr1 (= fr0) to transmit a large amount of power. Is interpreted as possible. However, it was found that even if the wireless power feeding device 116 does not include the power feeding LC resonance circuit 300, the magnetic field resonance type wireless power feeding can be realized as long as the wireless power receiving device 118 includes the power receiving LC resonance circuit 302.--Neotesla (talk) 01:31, 20 February 2022 (UTC)
 * However, before TDK became aware of this fact, Japan's DAIFUKU, Aichi Electric, Sinfonia Technology, etc. had already been put into practical use industrially.--Neotesla (talk) 22:46, 9 November 2022 (UTC)

How does the generation of amplitude modulation gets avoided?
Normally coupled oscillators create amplitude modulation if they are in in resonance. Should that be explained to? Quaderratistteuer (talk) 19:40, 30 September 2020 (UTC)


 * One solution is to remove the primary resonator.
 * The causing of the amplitude modulation is that
 * the difference between the resonance frequency of the primary side $$\omega_1$$ and the secondary side $$\omega_2$$, and the non-linear characteristics of the rectifier circuit. Modulation occurs when these two factors interact.
 * $$\omega_1 = {1 \over \sqrt{{L_1} C_1}}$$　$$\omega_2 = {1 \over \sqrt{(1-k^2)\cdot{L_2} C_2}}$$
 * $$\omega_1 < \omega_2$$
 * Here, if the resonant circuit is only on the secondary side, no modulation will occur. If the coupling coefficient $$k$$ is over than 0.1, the resonant circuit can be enough only on the secondary side. Nevertheless high efficiency power transfer is possible. Neotesla (talk) 16:12, 16 November 2022 (UTC)